MAROELLUS LIMESTONES OF LANCASTER 173 



this species show the protuberant glabella characteristic of 

 Phacops cristata, but the lateral crenulations of the sub- 

 marginal furrow are absent, and other features characteri-stic of 

 the species are not shown. 



cRYPHAEus Green 

 Cryphaeus boothi Green 



Pal. N. Y. 7:42, pi. 16, 16a 



This is a rare species at Plumbottom creek. It is represented 

 bj fragments of the cephalon and pygidinm. A small specimen 

 in bed V shows the genal spines and strongly pustulose glabella. 



CYPHASPis Burmeister 

 Cyphaspis craspedota Hall 



Pal. N. Y. 7:148, pi. 24 



A few specimens of this species have been found in beds V 

 and VII. A cephalon from bed V shows the pustulose glabella, 

 palpebral lobes, marginal sulcus and one genal spine. It is 4 

 mm long, and 8 mm wide. The spine is 2.8 mm in length. 



OSTRACODA 



pRiMiTiopsis Jones 

 Primitiopsis punctulifera Hall 



N. Y. state mus. 13th an. rep't. 1860. p. 92 



This is a rare fossil at this locality, but when found the shells 

 are usually well preserved, showing the form and reticulated 

 surface markings. 



'&> 



From a consideration of the lithologic character of the dif- 

 ferent beds, at this locality, and the size and distribution of the 

 contained fossils, successive changes in physical conditions may 

 be inferred. Though the change from shale to limestone was 

 a somewhat abrupt one, the limestone at first retained consider- 

 able' carbonaceous material, as shown by the dark color and 

 limited number of species in bed I. In beds II and III a gradual 

 clearing of the water is indicated by the increasing purity of the 



